The present invention relates to cutting inserts having cutting edges formed from a superhard abrasive material, and methods of making the same.
In the description of the background of the present invention that follows reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
Indexable cutting inserts using a superhard material for cutting typically have a polygonal shape with the superhard material disposed at the corners of the polygon. The superhard material, often a cubic boron nitride or polycrystalline diamond material, aids in the cutting of hard workpiece materials such as metals. These cutting inserts are typically mounted in a fixed position to a cutting tool so as to present one of the corners or areas containing superhard material to the surface of a workpiece. After being used for a period of time, the area of superhard material becomes worn. The cutting insert can then be unfastened from the cutting tool and rotated so as to present a new fresh corner or area of superhard material to the surface of the workpiece.
There are two predominant ways of making such inserts. According to one technique, a stacked structure is formed comprising a first layer of hard backing material and a layer of superhard cutting material superimposed onto the backing layer. Cutting tips are then cut from this stacked structure and brazed to a cutting insert body, typically at a corner thereof. U.S. Pat. No. 5,183,362 to Kuroyama et al., the disclosure of which is incorporated herein by reference, in its entirety, describes such a technique.
A second technique for forming indexable cutting inserts involves providing a blank or substrate having pockets formed therein which are filled with superhard material, then subjecting the blank to a sintering operation which bonds the superhard material to the substrate. The blank is then subsequently machined to give the cutting insert its final shape, i.e.—a generally polygonal body with superhard material disposed at the corners thereof. U.S. Pat. No. 5,676,496, the disclosure of which is incorporated herein by reference, in its entirety, describes such a technique.
In general, such superhard material-containing inserts have been held in place by an external (e.g., top) clamp. See, for example, FIG. 25 of U.S. Pat. No. 5,183,362 which shows a top clamp with a preformed, separate chip breaker. Another type of clamping used with other types of cutting inserts involves the use of a screw which passes through a hole in the insert, often in the center of the insert. Such holes may be straight or involve an offset portion to assist in securing the insert. See, for example, U.S. Pat. No. 5,147,158 which discloses in cross-section a “trumpet” style of clamping hole for securing purposes. Laser cutting or EDM (electro-discharge machining) is used to cut the superhard material and it can be appreciated that machining of a “trumpet” style hole in the superhard material is quite difficult and expensive to do. In addition, the accuracy of such cuts is problematic.
In U.S. Pat. No. 6,120,570, there is a disclosed a method of making a cutting insert of a superhard material which is sintered onto a cemented carbide base by high pressure and temperature. A hole is simultaneously formed in the insert through the use of a plug, preferably made of the same cemented carbide as the base, which is not bonded to the insert but is removed after sintering. In FIG. 3 of U.S. Pat. No. 6,120,570, the hole is shown to be tapered towards the bottom of the insert.
U.S. Pat. No. 5,536,119 shows a conventional cutting insert in which a through hole has an upper part which is substantially cylindrical while the remaining part tapers downwardly in the form of a convexly vaulted surface.
Thus, a need exists in the art to address the problems discussed above and others.